The document explains Docker Compose, a tool for defining and running multi-container Docker applications. It allows users to configure application services using a YAML file and run them using a single command. The document provides examples of Docker Compose files for running simple applications with 2 or more containers, and converting a Docker run command to a Docker Compose file. It also lists some common Docker Compose subcommands.

1. DockerCompose
Explained

2. - A simple command to start a container
- options are available through command line parameters
- options specified here are:
- d -- detached
- i -- interactive
- t -- assign a tty
- --name -- assigns a name to the running image
- these options may sound contradictory, the result leaves a
running image
- there's a point where rerunning with all the options does get
cumbersome
- at this point a shell script is a viable solution
dockerisgoodforonecontainer
docker run
-dit
--name metacpan-api
metacpan-api:latest
/bin/bash

3. - Two containers isn't too bad to
manage
- running both from the shell with
an && to ensure proper starting
order
- same caveat, lots of options
could require a shell script
ortwocontainers
docker run -d
--name metacpan-pgdb
metacpan-pgdb:latest
&&
docker run -d
--name metacpan-api
metacpan-api:latest

4. - metacpan has 5 different containers
- 2 elasticsearch
- 1 postgresql
- 1 api
- 1 web
- networks
- elasticsearch
- web
- database
- mounted volumes
- more than I care to count
Butwhathappenswhenyouhave5?

5. - Our current project has 45
different containers
- as a side note these details
can be obtained by running
docker-compose config
--services
Or45?

6. - Compose is a tool for defining and
running multi-container Docker
applications.
- YAML file to configure your
applicationʼs services.
- single command, you create and
start all the services from your
configuration.
Whatis
docker-compose

7. - this is a very simplistic model
- 2 containers, web & api
- the version number here is
significant
- the depends_on attribute
automatically starts api if we only
start web
Simple docker-compose.yml
version: "3.4"
services:
web:
image: metacpan-web:lastest
depends_on:
- api
api:
image: metacpan-api:lastest

8. - version 3.0 indiciates Docker Engine relase
1.33.0+
- version 3.7 indiciates Docker Engine relase
18.06.0+
- what attributes are available to be defined varies
greatly
- healthcheck for example is only supported
from version 2.1
- while mounting volumes read-only is only
available in 3.4
A word about version numbers
· Dictates the version of docker
· Indicative of the attributes available

9. - A little side story
- I had intended to use reveal.js for this presentation
- the formatting and code highlighting really bugged me
- I've reverted back to using DeckSet
- but had I continue...
- this is the run command suggested for running this
presentation in a container
- there are a lot of volumes to be mounted, and rerunning
by hand is definitely not something you'd want to do
- docker image is from https://github.com/
nbrownuk/docker-revealjs
Example of docker run with many options
docker run -it --rm -p 8000:8000
-v $PWD/index.html:/reveal.js/index.html
-v $PWD/media:/reveal.js/media
-v $PWD/custom.css:/reveal.js/css/theme/custom.css
-v $PWD/menu:/reveal.js/plugin/menu
nbrown/revealjs
Docker image is from https://github.com/
nbrownuk/docker-revealjs

10. - let's convert the docker run
command from the previous
slide into a working docker-
compose.yml
Exercise

11. - when doing a conversion I
like to keep the code that I'm
replacing local
- I comment it out and delete
the bits I'm working on and
paste them in the real code
Converting a docker run command
# docker run -it --rm -p 8000:8000
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
# nbrown/revealjs

12. - start off with the required bits
- specify the version of the file (I
want read-only mounts)
- start the services definitions
- name the service reveal in
this case
Converting a docker run command
# docker run -it --rm -p 8000:8000
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
# nbrown/revealjs
version: "3.4"
services:
reveal:

13. - we're going to define the
image
Converting a docker run command
# docker run -it --rm -p 8000:8000
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
# nbrown/revealjs
version: "3.4"
services:
reveal:
image: nbrown/revealjs:latest

14. - we're going to define the ports in use
- the first port is the external listening port, the
second is the internal
- this is used for when you want to access a
container from the host
- for the presentation I want to point my browser
at 127.0.0.1:8000
- while I'm removing the ports definition from the
run command, I'm going to remove the run
command
Converting a docker run command
# docker run -it --rm -p 8000:8000
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
#
version: "3.4"
services:
reveal:
image: nbrown/revealjs:latest
ports:
- 8000:8000

15. - What I'm left with here are
the volumes
Converting a docker run command
#
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
#
version: "3.4"
services:
reveal:
image: nbrown/revealjs:latest
ports:
- 8000:8000
volumes:

16. - What I'm left with here are
the volumes
Converting a docker run command
#
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
#
version: "3.4"
services:
reveal:
image: nbrown/revealjs:latest
ports:
- 8000:8000
volumes:

17. - the first volume is for the index.html
- docker volumes are defined source:destination
on the command line
- In the docker-compose, I'm using expanded syntax as
it's easier to read and allows for more options
- type is bind, because we're specifically mounting a
file, a remote volume would be type volume
- source - while docker-compose supports environment
variables and other variables, it's not required here
- destination - this is where the application in the
container is expecting the file to be
Converting a docker run command
#
# -v $PWD/index.html:/reveal.js/index.html
# -v $PWD/media:/reveal.js/media
# -v $PWD/custom.css:/reveal.js/css/theme/custom.css
# -v $PWD/menu:/reveal.js/plugin/menu
#
version: "3.4"
services:
reveal:
image: nbrown/revealjs:latest
ports:
- 8000:8000
volumes:
- type: bind
source: ./index.html
target: /reveal.js/index.html
read_only: true

18. Complete docker-compose.yml
version: "3.4"
services:
reveal:
image: nbrown/revealjs:latest
ports:
- 8000:8000
volumes:
- type: bind
source: ./index.html
target: /reveal.js/index.html
read_only: true
- type: bind
source: ./media
target: /reveal.js/media
read_only: true
- type: bind
source: ./custom.css
target: /reveal.js/css/theme/custom.css
read_only: true
- type: bind
source: ./menu
target: /reveal.js/plugin/menu
read_only: true
- type: bind
source: ./md
target: /reveal.js/md
read_only: true

19. - without the -d option docker-compose up will
start containers and logging in the foreground
- the --volumes options to docker-compose down
removes any persistent storage volumes that are defined
- useful if you can recreate your database from scratch
- log is extremely useful if you've started containers in
detached mode, it also supports -f just like tail
- docker-compose was originally called fig, which is a
lot less typing
- create an alias, save your fingers
Simple Commands
· docker-compose up
builds creates/recreates and attaches to containers
· docker-compose down
stops and removes containers, networks and volumes
· docker-compose stop
stops containers without removing them
· docker-compose start
starts existing containers for a service
· docker-compose log
starts existing containers for a service

20. Furtherreading
· Docker Compose documentation
https://docs.docker.com/v17.09/compose/
overview/`

21. END